Arrangement for supplying a user, especially a D.C motor, that consumes power in a non-continuous manner from a D.C. system

ABSTRACT

The invention concerns an arrangement for powering a load ( 12 ) that has non-continuous power consumption from a DC power supply (UB). The arrangement has a DC link circuit ( 14, 22 ) to which said load ( 12 ) can be connected and with which is associated a capacitor ( 21 ) that is suitable for briefly supplying energy to the load. A current regulator ( 24, 30 ) is provided for connecting the DC link circuit ( 14, 22 ) to the DC power supply (UB) in order to deliver a substantially constant current (i) to said capacitor ( 21 ) and to a load ( 12 ) connected to the link circuit. The target value of said current regulator ( 30 ) is adjusted adaptively, by means of a second regulator ( 34 ), to the instantaneous power demand of the load ( 12 ). An arrangement of this kind can also be referred to as an active filter that is particularly suitable for electronically commutated motors and for motors with a PWM current controller. The arrangement has an electronic fuse ( 240 ) which switches off the current regulator ( 30 ) when it responds and automatically switches the current regulator ( 30 ) back on after a defined time has elapsed, and repeats these switch-on attempts several times if applicable.

FIELD OF THE INVENTION

The invention concerns an arrangement for powering a load that hasnon-continuous power consumption, in particular a DC motor, from a DCpower supply.

BACKGROUND

In the telecommunications sector in particular, very stringentrequirements exist in terms of electromagnetic compatibility (EMC).Electric motors are often used in communication technology systems, e.g.to drive fans, and the output stages of such motors are supplied withpulsed currents, e.g. for current limiting (cf. FIG. 3 below). Thesepulsed currents cause pulse-containing interference signals on thesupply leads to such motors, and very large capacitors and inductancesare needed to suppress them. Installation space is often limited,however, and the cost of such filters is high.

The filtering of high-frequency interference generally presents no majorproblems. Particularly stringent requirements exist, however, in theaudible frequency range from 25 Hz to 20 kHz, since a humming backgroundnoise is particularly irritating when telephoning. The rotationfrequency of such motors lies in the range from 25 to 200 Hz. Thehighest interference level is therefore reached in this frequency range.It is no longer possible to filter out this low-frequency interferenceusing conventional filters.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to make available a newarrangement for powering a load that has non-continuous powerconsumption, in particular a DC motor, from a DC power supply, thattakes EMC requirements into account.

According to the invention, this object is achieved by means of anarrangement having a first regulator for supplying a substantiallyconstant current, via a transistor to the DC motor and a secondregulator which supplies a target value to the first regulator, basedupon a voltage at the DC motor, so that the target value isautomatically adapted to varying loads of the DC motor. Because acurrent regulator is used, the direct current that flows to anarrangement according to the present invention during operation has avery low residual ripple. During the time periods in which the load isbriefly consuming little or no current, for example because of a controloperation, the capacitor associated with the DC link circuit is chargedby the current regulator. When the load, typically an electronicallycommutated motor, briefly requires more current than can be madeavailable by the current regulator, this capacitor is partiallydischarged and delivers some of its energy to the load.

The DC voltage at the load thus has a small AC voltage componentsuperimposed on it, since the voltage at the capacitor fluctuatesbecause of these charging and discharging operations. But as long asthis AC voltage component, which is critically influenced by the size ofthe capacitor, is small compared to the DC voltage component, it has noinfluence e.g. on how the motor runs.

What is obtained by means of the invention is thus an active filter thatautomatically compensates for low-frequency fluctuations in the powerconsumption of a load, and therefore corresponds very closely to therequirements for electromagnetic compatibility. It is thereforeparticularly suitable for use in telecommunication systems.

The arrangement is advantageously designed so that the voltage drop atthe current regulator corresponds approximately to the AC voltagecomponent of the voltage at the DC link circuit. Surprisingly, this hasproven in tests to be very advantageous.

If the load is a motor and if its loading increases, the effect of thecurrent regulator would be to decrease the voltage at the motor becauseits rotation speed is decreasing, and the voltage and power dissipationin the current regulator would increase accordingly. The invention istherefore advantageously refined by making the target voltagesubstantially proportional to the voltage drop at the transistor servingas a linear adjusting element. As a result, the current regulatorautomatically adapts to the power demand of a motor, i.e. if therotation speed and voltage at the motor decrease, the target value ofthe current regulator is increased, and if the rotation speed andvoltage rise, the target value is reduced. This is therefore an adaptivecurrent regulator that automatically adapts to changes in power demandin a connected motor.

Further details and advantageous developments of the invention areevident from the exemplary embodiments, which are in no way to beunderstood as a limitation of the invention, that are described belowand depicted in the drawings.

BRIEF FIGURE DESCRIPTION

FIG. 1 is a block diagram of a first preferred embodiment of anarrangement according to the present invention;

FIG. 2 is a circuit diagram showing details of the exemplary embodimentof FIG. 1;

FIG. 3 is a oscillogram of the current, labeled i′ in FIG. 1, through aload 12, which in this exemplary embodiment is a two-pulse, two-phaseelectronically commutated motor as known in principle e.g. from DE 23 46380 and corresponding U.S. Pat. No. 3,873,897;

FIG. 4 is an oscillogram of the current, labeled i in FIGS. 1 and 2,through measuring resistor 26 of current regulator 30;

FIG. 5 is an oscillogram of the AC voltage component of the voltagelabeled UZK in FIGS. 1 and 2;

FIG. 6 is an oscillogram of the voltage, labeled UT in FIGS. 1 and 2,between drain D and source S of MOSFET 24;

FIG. 7 depicts a second exemplary embodiment of the invention, similarto FIG. 2;

FIG. 8 depicts a timing member used in FIG. 7;

FIG. 9 is a highly schematic depiction to explain a detail;

FIG. 10 shows a variant 10″ of FIG. 2 in which electronic fuse 240resets itself at regular intervals;

FIG. 11 is a diagram to explain the manner of operation of FIG. 10; and

FIG. 12 shows a variant of FIG. 2 or FIG. 10 having an emergency powersupply for the case in which MOSFET 24 becomes defective.

In the Figures hereinafter, the same reference characters are used foridentical or identically functioning parts, and the parts in questionare usually described only once.

DETAILED DESCRIPTION

FIG. 1 is an overview diagram of a first embodiment of an arrangement 10according to the present invention. It serves to operate a load withnon-continuous power consumption, in particular an electric motor 12 ofany kind, from a DC voltage UB to which said arrangement is connected bymeans of a positive line 14 and a negative line 16. In this embodiment,positive line 14 is the reference potential line and is connected toground 17. A protective diode 19 is present in negative line 16 forprotection against improperly polarized connection. Lines 14, 16 can beconnected e.g. to a 48-volt battery 15 (FIG. 2) or to an appropriatepower supply section. Motor 12 is connected to two outputs 18, 20 ofarrangement 10. Output 18 is connected directly to positive line 14, andoutput 20 to a link circuit voltage 22. Located between outputs 18 and20 is a high-capacitance capacitor 21, associated with the DC linkcircuit, that serves as an energy reservoir for load 12.

Located between node 20 and negative line 16 are an N-channel fieldeffect transistor 24 and, in series therewith, a resistor 26 whichserves to sense the current i that flows through measuring resistor 26,said current being regulated by arrangement 10 to a substantiallyconstant value.

In the exemplary embodiment of FIGS. 1 through 6, supply line 14 is thereference potential line and an active filter 24, 30 is arranged innegative supply line 16 of motor 12. The reason for this is that thetelecommunications industry normally operates with a supply voltage of−48 V, so that the reference potential of 0 V, i.e. the potential online 14, is positive. Control signals are referred to this +0 Vpotential. Protective diode 19 is located in the negative supply line sothat no voltage drops occur on reference potential line 14. If a motor12 with a negative reference potential needs to be used, an activefilter arranged in the positive branch of motor 12 should be utilized,and in this case negative line 16 is connected to ground. This is shownin FIGS. 7 and 8.

A link circuit voltage UZK is obtained between lines 14 and 22. Avoltage UT, which is measured between drain D and source S of transistor24, occurs at transistor 24 (which is operated as a variable resistor);and a voltage UR whose magnitude depends on the current i is obtained atresistor 26. The operating voltage UB can thus be described as follows:

UB=UZK+UT+UR  (1)

Since UR is usually very small, it is approximately the case that

UB=UZK+UT  (2)

The working principle of the present arrangement is that by means of acurrent regulator 30, the current i through transistor 24 is regulatedto a target value 32 that is constant when the load of motor 12 isconstant. As a result, a substantially constant and harmonic-free directcurrent i flows on supply leads 14, 16 of arrangement 10.

If the load on motor 12 changes, target value 32 for current regulator30 is correspondingly modified by means of a second regulator referredto hereinafter as link circuit regulator 34. For example, if motor 12slows down because of an increased load, voltage UZK then drops, i.e.voltage UT increases as shown in equation (2). The sum of voltages UTand UR is delivered to link circuit regulator 34, which then increasesthe current target value 32 of current regulator 30 so that the latteradjusts transistor 24 to a higher current, i.e. a lower resistance,thereby once again increasing the rotation speed of motor 12 and at thesame time preventing an overload of transistor 24, since voltage UTthere decreases again. (The losses in transistor 24 correspond to theproduct i * UT, and these losses must not exceed a specific value.)

The arrangement shown in FIG. 1 also comprises a limitation of thecurrent target value at input 32, depicted here symbolically as Zenerdiode 36. This limits current target value 32 to a permissible value asmotor 12 starts, in order to prevent an overload of transistor 24 due toa high start-up current. The same is true in the context of a shortcircuit. This system also automatically limits a current that occursupon start-up due to the charging of capacitor 21. That current wouldotherwise be limited only by the resistance of supply lines 14, 16 andby resistor 26, which together have a value of e.g. 0.5 ohms. For UB=50V this would result (without current limiting) in a start-up current of50/0.5=100 A, which could cause damage to switch contacts.

An overvoltage protector 38 is preferably also provided for protectionagainst excessive values of voltage UB. It acts directly or indirectlyon gate G of transistor 24 in order to discharge the latter uponoccurrence of an overvoltage pulse, thereby limiting voltage UZK atmotor 12 and protecting it from damage due to overvoltage.

In addition, a fuse function 40 is preferably also provided in order toprotect transistor 24 from overload. If voltage UT rises above a definedvalue that corresponds to a value higher than that specified by themaximum target value 32 at the output of link circuit regulator 34,transistor 24 is switched off directly at its gate G after a definedtime interval. The defined time is selected so that transistor 24 cannotheat up excessively. In order to switch motor 12 on again after fuse 40has responded, arrangement 10 must be briefly switched off. Thistherefore corresponds to the principle of an electronic fuse.

In exemplary and highly schematic fashion, FIG. 1 shows motor 12 as partof a motor arrangement 44 in which motor 12 drives a load 46, forexample a fan wheel. Current i′ through motor 12 is sensed at a resistor54 and conveyed to a regulator 52 in order to limit said current i′ atstartup of motor 12. Current i′ through motor 12 which can occur atstartup as a result of the internal current limitation of arrangement 44is preferably set to be lower than the maximum value of current i thatdoes not yet result in triggering of electronic fuse 40. The result isthat electronic fuse 40 responds only in the event of a fault.

Such operations (current limiting) are today often performed using a PWMcontroller, so that current i′ in motor 12 takes the form of shortpulses (see FIG. 3). If motor 12 is an electronically commutated motor,current i′ through the motor takes the form of low-frequency pulses (ata frequency in the range of 25 to 200 Hz) even without a PWM controller.Pulses of this kind create problems in many applications, e.g. intelecommunications systems. With conventional filters, it is almostimpossible in practice to filter out such low-frequency interference; inother words, electromagnetic compatibility (EMC) requirements arepractically impossible to meet for the lower frequencies usingconventional means.

FIG. 3 shows a typical example of a motor current i′ that takes the formof short pulses at relatively high frequency, superimposed on which is alow-frequency component caused by commutation of electronicallycommutated motor 12, so that at regular intervals (points 53) current i′becomes zero. The low-frequency component usually has a frequency in therange 25-200 Hz.

The procedure according to the invention is therefore that current i isregulated by current regulator 24, 30 to a constant value. At points 53at which motor 12 is consuming very little or no current, capacitor 21is charged by current regulator 24, 30.

At points 55 (FIG. 3) where motor 12 has a high current consumption, themotor is powered partly via current regulator 24, 30 and partly fromcapacitor 21. The consequence is that a rippled DC voltage, i.e. a DCvoltage with a small superimposed AC voltage component, occurs atcapacitor 21. This AC voltage component uzkw is depicted in FIG. 5. Itsupper peak value is e.g. +0.5 V, and its lower peak value −0.5 V.Electronically commutated DC motors, in particular, are relativelyinsensitive to a superimposed AC voltage of this kind.

FIG. 4 shows current i through resistor 26, which in an arrangement ofthis kind has a largely constant value. FIGS. 3 and 4 use the same scalefor the time axis t and for the values of currents i′ and i, and theenormous improvement resulting from the present invention is evident. InFIG. 4, for example, current i is approx. 0.6 A, whereas the peak valuesof current I′ occurring in motor 12 itself are up to 2.7 A.

Arrangement 10 or 10′ (FIG. 7) is preferably designed in such a way thatthe AC voltage component of voltage UT corresponds approximately to theAC voltage component uzkw of voltage UZK, e.g. 1 V. Superimposed on thelatter value, as the so-called offset, is the voltage drop of approx.1.5 V at the semiconductor sections of transistor 24, so that UTfluctuates e.g. between 2 and 3 V, as depicted in FIG. 6. That value ofUT is advantageous also because the current to motor 12 can decreasebriefly, and in such a case capacitor 21 should not be fully charged,since it must then briefly accept the regulated current i from currentregulator 24, 30. This is referred to as a control reserve. In the caseof a fan, for example, a gust of air can briefly decrease the powerdemand, and a portion of the regulated current then flows into capacitor21, thereby raising UZK and correspondingly lowering UT.

An arrangement 10 or 10′ according to the present invention can also bereferred to as an “active filter,” since it actively filters outinterference pulses that otherwise would occur on supply lines 14, 16.

FIG. 2 shows a first preferred embodiment of the present invention.Diode 19 is located in negative line 16. The arrangement as shown inFIG. 2 or 7 can also be incorporated directly into a motor 44 ifparticularly stringent requirements exist regarding the electromagneticcompatibility of that motor.

From positive line 14, a resistor 62 leads via a node 64 to a Zenerdiode 66 whose anode is connected to negative line 16. Connected to node64 is the base of an npn transistor 68 that is wired as an emitterfollower, so that the potential +Vss at its emitter correspondssubstantially to the potential at node 64. Its collector is connectedvia a resistor 70 to positive line 14. The result is to produce at theemitter of transistor 68 a regulated DC voltage that serves, inter alia,to supply power to three operational amplifiers (OAs) 74, 76, and 78,this being depicted only for OA 78. The latter is thus connected topotential +Vss and to negative line 16, i.e. to potentials of e.g. −36 Vand −48 V, referred to positive line 14 with its potential of 0 V.

Gate G of N-channel MOSFET 24 is connected via a resistor 80 to output79 of OA 78. Transistor 24 is conductive when this output is high, andblocked when it is low. In the region between high and low, transistor24 acts as a variable resistor whose value can be modified by thevoltage at gate G. A transistor of this kind is said to “operate inlinear mode.”

Source S of transistor 24 is connected via current sensing resistor 26to negative line 16, and additionally via a resistor 82 to the negativeinput of OA 78, which in turn is connected to output 79 via a resistor84 and a capacitor 86 in parallel therewith.

Negative line 16 is connected, via a resistor 88 and a capacitor 90 inparallel therewith, to positive input 32 of OA 78, to which a currenttarget value is delivered from the output of OA 76 via a resistor 118.Also connected to positive input 32 is the collector of an npntransistor 92 that is part of electronic fuse 40.

The output of OA 76 is connected via a negative feedback resistor 122 toits negative input, which is connected via a resistor 120 to negativeline 16. The positive input of OA 76 is connected via a resistor 116 anda node 114 to line 22, i.e. to link circuit voltage UZK.

The emitter of transistor 92 is connected to negative line 16. Its baseis connected via a resistor 94 to negative line 16 and via a resistor 96to a node 98, which in turn is connected via a capacitor 100 to negativeline 16 and via a resistor 102 to the output of OA 74 (connected as acomparator).

Negative input 104 of comparator 74 is connected via a resistor 106 tonegative line 16, and via a resistor 108 to regulated voltage Vss.Negative input 104 is thus at a constant reference potential. Positiveinput 110 of comparator 74 is connected via a resistor 112 to node 114,which is connected to link circuit line 22.

The collector of transistor 92, as well as the collector of an npntransistor 126, is connected to node 32. The emitter of transistor 126is connected to negative line 16. Its base is connected via a resistor128 to a node 130, which in turn is connected via a resistor 132 tonegative line 16 and via a Zener diode 134 to positive line 14.

Manner of Operation

Upward limitation of the current target value, namely voltage u32 atresistor 88 is established by way of the values of resistors 118 and 88.The maximum output voltage of OA 76 corresponds to the supply voltageVss (e.g. +12 V) that is delivered to said OA. The upper limit value ofcurrent target value u32 can be set very precisely by way of the ratioof resistors 118 and 88, since it is defined as

u32=Vss*R88/(R118+R88)  (3)

Alternatively, a Zener diode could also be used instead of resistor 88,but that imposes a limitation to specific voltage values, and the upperlimit value of u32 can be set much more precisely using the voltagedivider just described.

During operation, current i causes a voltage drop u26 at measuringresistor 26, and the difference (u32−u26) is amplified by OA 78 andintegrated by capacitor 86. The integration yields, at output 79 of OA78, a DC voltage signal that linearly controls field effect transistor24 via resistor 80.

If, for example, voltage u26 (which serves as the true current valuesignal) is lower than voltage u32, i.e. if the potential at the positiveinput of OA 78 is higher than the potential at the negative input, theDC voltage at the output of OA 78 is increased and transistor 24experiences greater activation, so that current i becomes higher.Conversely, if voltage u26 is greater than u32, current i throughtransistor 24 is then reduced, so that said current i is thereforeregulated by current regulator 30 to a constant value.

Current regulator 30 has a PT1 characteristic, i.e. the characteristicof a proportional controller with a first-order timing member. The gainfactor is

Kp=−R84/R82  (4),

and the time constant T1 is

T1=R84*C86  (5).

Link Circuit Regulator 34

Voltage UT at transistor 24 is conveyed via resistor 116 to the positiveinput of OA 76 and amplified. The latter is once again a proportionalcontroller with a first-order timing member, i.e. a PT1 controller. Itsgain factor Kp is

Kp=R122/R120  (6)

Whereas timing member 84, 86 in current regulator 30 is implemented asan active timing member in the negative feedback from output 79 to thenegative input of OA 78, in link circuit regulator 34 it is arrangedpassively at the output of OA 76 (resistors 118, 88 and capacitor 90).This has the advantage that any interference is thereby simultaneouslyfiltered out from overvoltage shutoff 38 and fuse function 40.

If voltage UT rises (i.e. voltage UZK decreases) as a result of anincreasing load on motor 12, OA 76 generates a higher potential at itsoutput, i.e. target value u32 for current regulator 34 is raised. In themanner already described, the upper limit of this target value isdefined by the ratio of resistors 118 and 88.

When target value u32 rises as a result, transistor 24 becomes moreconductive, so that voltage UT once again decreases and voltage UZKincreases.

Since link circuit regulator 34 has a higher time constant than currentregulator 30 because of capacitor 90 (e.g. 3.3 uF), it reacts only tolonger-lasting changes in UT or UZK. This has proven to be advantageousso that the arrangement described here does not tend to oscillate; inother words, link circuit regulator 34 should react only slowly in orderto ensure the desired adaptive behavior.

Because current regulator 30 acts directly on the input of supplyvoltage UB, it is not only the starting current of motor 12 that islimited, but also the startup current pulse that occurs upon startup asa result of the charging of capacitor 21, which otherwise could assumelarge values (e.g. 100 A).

Fuse Function 40

Voltage UT is conveyed from line 22 via resistor 112 to the positiveinput of comparator 74. As already described, a constant potentialdefined by the ratio of resistors 106, 108 is present at negative input104.

If the potential at positive input 110 becomes higher than the potentialat negative input 104, the output of comparator 74 then becomes high andcapacitor 100 is charged through resistor 102. Resistor 102 andcapacitor 100 constitute a first-order timing member which determinesthe time required by transistor 92 to become fully conductive, i.e. thetime until the fuse function responds, and its sensitivity. Thesensitivity of fuse function 40 can be modified in the desired fashionby dimensioning resistor 102 and capacitor 100.

When transistor 92 becomes conductive it reduces voltage u32, so thattransistor 24 becomes less conductive. As soon as transistor 24 hasswitched off completely, a “high” potential is continuously present atthe positive input of comparator 74; as a result, comparator 74 goesinto “latch” mode and arrangement 10 is permanently switched off. Inorder to be switched on again, the entire arrangement 10 must beswitched off and then switched back on.

Overvoltage Protector 38

In the event of short-term voltage spikes in voltage UB, Zener diode 134becomes conductive and makes transistor 126 conductive, so that voltageu32 is correspondingly reduced and transistor 24 becomes lessconductive. Voltage spikes of this kind thus do not affect motor 12. Ifthe overvoltage persists for a longer period, fuse function 40 takeseffect and switches off motor 12 in the manner already described.

FIG. 5 shows the changes in the AC voltage component of voltage UZK thatoccur at capacitor 21 during operation of motor 12. This (small) ACvoltage component is superimposed on the DC voltage at motor 12. Itconstitutes, for example, 2% of voltage UZK.

FIG. 6 shows the changes in voltage UT, which fluctuates continuallybetween a maximum value 140 and a minimum value 142.

EXAMPLES OF VALUES FOR FIG. 2

UB 48 V (38-72 V) Power consumption of motor 12 30 W (0-60 W)Operational amplifiers 74, 76, 78 LM2902D Transistors 92, 126 BC846BTransistor 68 BST39 Transistor 24 IRF640 Zener diode 66 BZX284C12 Zenerdiode 134 BZD27C82 Capacitor 21 470 uF Capacitor 100 1 uF Capacitor 903.3 uF Capacitor 86 4.7 nF Resistors 62, 108, 112, 120, 122, 128 10kOhms Resistor 70 1 kOhm Resistor 132 120 kOhms Resistor 94 11 kOhmsResistor 96 82 kOhms Resistors 102, 116 100 kOhms Resistor 106 4.7 kOhmsResistor 118 39 kOhms Resistor 78 7.5 kOhms Resistor 84 22 kOhmsResistor 82 4.7 kOhms Resistor 26 77 Ohms Resistor 80 1 kOhm Resistor 885.1 kOhms

FIG. 7 shows an arrangement 10′ in which the current regulator isarranged in positive supply line 14, while negative supply line 16serves as reference potential and is connected to ground 17. Only theessential functions are explicitly depicted in FIG. 7. Protective diode19′ is located in positive supply line 14 in this instance.

Located once again at the extreme left is battery 15, e.g. 48 V, andnext to it a power supply section 140 which generates at its output 141a voltage Vss that e.g. is 12 V lower than the potential of positiveline 14. The reader is referred to the description of parts 62, 66, 68,70 of FIG. 2 regarding the manner of operation of the power supplysection.

A link circuit regulator 144 is located to the right of power supplysection 140, and a current regulator 146 to the right of that. The motoris once again labeled 12, and the link circuit capacitor 21.

Connected to motor 12 via a node 149 is a P-channel field effecttransistor 150 whose drain D is connected to a node 149, and whosesource S is connected via a node 151 and a measuring resistor 152 topositive line 14. At measuring resistor 152, current i during operationcauses a voltage drop u152 which is regulated by current regulator 146to a value corresponding to a target value u188 that is defined forcurrent regulator 146 by link circuit regulator 144. Link circuitregulator 144 generates this target value in dependence on the magnitudeof (u152+UT), i.e. if this value rises because voltage UZK at motor 12decreases, the target value for current regulator 146 is increased; andif that voltage drops, target value u188 is reduced. What is therebyobtained is an adaptive control system, i.e. current regulator 146adjusts itself adaptively (i.e. slowly) to the power demand of motor 12.

Arrangement 10′ uses two OAs 160, 162 that, for voltage supply purposes,are connected in the manner depicted to positive line 14 and to output141 of power supply section 140, and consequently are at an operatingvoltage of e.g. 12 V, i.e. at potentials of +48 V (line 14) and +36 V(line 141).

Output 163 of OA 162 is connected via a resistor 166 to gate G oftransistor 150. It is additionally connected via a resistor 168 tonegative input 172 of OA 162. A capacitor 170 is connected in parallelwith resistor 168, and these together constitute an active timing memberin the form of a negative feedback for OA 162. Negative input 172 isadditionally connected via a resistor 174 to node 151 and via a resistor176 to line 141 (Vss). Also connected to input 172 is a timing member175 which is depicted in FIG. 8 and whose purpose is to block transistor150 until a capacitor 177 of power supply section 140 has charged to itsoperating voltage. Without timing member 175, transistor 150 would befully conductive immediately after arrangement 10′ is switched on, whichwould result in a large charging current to capacitor 21.

If current i increases, voltage u152 becomes greater and the potentialof node 151 therefore becomes more negative. Negative input 172 thusalso becomes more negative, depending on the voltage divider ratio ofresistors 174 and 176. In this fashion, actual value u152 thus also actson negative input 172 of operational amplifier 162.

Positive input 180 of OA 162 is connected to positive line 14 via aresistor 182, to output 186 of OA 160 via a resistor 184, and to line141 via a resistor 188 and a capacitor 190 connected in paralleltherewith. Capacitor 190 and resistor 188 form a timing member forregulator 144. A functional unit 192, e.g. an electronic fuse (40 inFIG. 1) or an overvoltage protector (38 in FIG. 1), can also beconnected to input 180.

Output 186 of OA 160 is connected via a negative feedback resistor 194to its negative input 196, which in turn is connected via a resistor 198to a node 200 that is connected via a resistor 202 to positive line 14and via a resistor 204 to line 141. Node 200 has a constant potential,so that negative input 196 is at a reference potential.

Positive input 206 of OA 160 is connected via a resistor 208 to line 141and via a resistor 210 to node 149. The voltage at the link circuit ofmotor 12 is thereby delivered to input 206.

Resistors 184, 188 determine, by means of their ratio, the maximum valueof voltage u188 which is delivered to input 180 of current regulator 146as the target value. Specifically, the maximum potential of output 186of OA 160 can be that of positive line 14, and the minimum that of line141; in the former case the voltage is

u188=Vss*R188/(R184+R188)  (7)

This defines the maximum value of current i.

Voltage u188 is conveyed to input 180 of OA 162; and if input 180 has amore positive potential than input 172, the current in transistor 150 isreduced until the potential at input 172 corresponds substantially tothe potential at input 180.

Conversely, if the potential at input 180 is more negative than thepotential at input 172, the current in transistor 150 is then increaseduntil the potential at input 172 substantially corresponds to thepotential at input 180.

Target value u188 and actual value u152 thus act on different inputs ofOA 162.

If the rotation speed of motor 12 decreases because of a load, voltageUZK then decreases and voltage UT rises correspondingly. The potentialat node 149 is conveyed via resistor 210 to input 206 of OA 160, and thepotential difference between inputs 196, 206 thus increases, causingoutput 186 to become more positive and u188 to rise. The consequence ofthis is that current i through transistor 150 is increased in the manneralready described, thereby causing UZK once again to rise.

The two regulators 144 and 146 are thus proportional controllers with afirst-order timing member (called PT1 controllers), although the timeconstant of regulator 144 is greater than that of regulator 146 becauseregulator 144 is intended to react only slowly, while regulator 146should react very quickly.

FIG. 8 shows the configuration of timing member 175 used in FIG. 7,which blocks transistor 150 for a defined period of time after startupuntil arrangement 10′ is fully activated. A timing member of this kindis not absolutely necessary in arrangement 10 as shown in FIG. 2.

A capacitor 220 is arranged between a node 222 and positive line 14.From node 222, a resistor 224 leads to line 141 and a resistor 226 tothe base of a pnp transistor 228 that is connected via a resistor 230 topositive line 14, to which the emitter of transistor 228 is alsoconnected. Its collector is connected via a resistor 232 to line 141 andvia a resistor 234 to the base of a pnp transistor 236 that is connectedvia a resistor 238 to positive line 14, to which the emitter oftransistor 236 is also connected. Its collector is connected to terminal172 of OA 162.

At startup, the discharged capacitor 220 represents a short circuit forresistors 226, 230, so that transistor 228 initially remains blocked.When capacitor 220 has charged to a defined voltage, this is sufficientto make transistor 228 conductive. As a result, the latter constitutes ashort circuit for resistors 234, 238 so that the previously conductivetransistor 236 now becomes blocked.

As long as transistor 236 is conductive, negative input 172 of OA 162receives the potential of positive line 162, thereby blocking transistor150. When transistor 236 becomes nonconductive, it has no furtherinfluence on current regulator 146, and the latter then operatesnormally and also limits the charging current of capacitor 21 thatoccurs at startup, which without such limitation could assume very highvalues.

UB 48 V (38-72 V) Power consumption of motor 12 30 W (0-60 W) OAs 160,162 LM324 Transistor 150 IRF9130 Transistors 228, 236 BC558A Capacitor21 1000 uF Resistor 152 0.33 Ohms Resistors 202, 204, 224, 232, 234, 23810 kOhms Resistor 194 11 kOhms Resistor 174 4.7 kOhms Resistor 168 16kOhms Resistor 166 1 kOhm Resistor 176 13 kOhms Resistor 182 54 kOhmsResistor 188 130 kOhms Resistor 184 82 kOhms Resistor 208 560 kOmsResistor 210 100 kOhms Resistor 226 6.8 kOhms Resistor 230 2.2 kOhmsCapacitor 170 4.7 nF Capacitors 177, 190 3.3 uF Capacitor 220 2 uF

An arrangement according to the present invention can yield thefollowing advantages, among others:

The regulated current i is dependent on the load on motor 12 (adaptivecharacteristic of regulator).

Current regulation is preferably accomplished with a MOSFET that isoperated as a variable resistor (“linear regulation”).

Voltage UZK at the link circuit is preferably sensed not directly, butrather indirectly via voltage UT at transistor 24 or 150. This ispossible because in this operating mode voltage UR is largely constant,and because transistor 24 or 150 is linearly regulated.

The maximum target value of current regulator 30 (at its input 32) or147 (at its input 180) is limited to a defined value. In the context ofa motor, this can be used to limit the starting current. Another resultthereof is to limit the startup current caused by the charging ofcapacitor 21, which otherwise could reach very high values.

Upon occurrence of a fault, e.g. a short circuit, the current limitationfunction mentioned in the item above is active for a longer time. Inorder to prevent overloading of MOSFET 24 or 150, the latter is thencompletely switched off after a defined time has elapsed. Switching offthe supply voltage allows arrangement 10 or 10′ to be activated again.

If voltage spikes occur, voltage UZK at motor 12 is limited by way ofthe linearly regulated MOSFET 24 or 150.

The principle described here of an active EMC filter can be used both innegative line 16 and in positive line 14 of supply voltage UB. FIGS. 1and 2 show an example of an active filter in the negative line, andFIGS. 7 and 8 an example of an active filter in positive supply line 14.

Because no inductances or other conventional filter elements arerequired in the context of the invention in order to filter the current,it is possible to transfer control signals for motor 12 on supply line14 (referring to FIG. 2) and on supply line 16 (referring to FIG. 7).

FIG. 9 shows, in highly schematic fashion, the transfer of a controlsignal Us in an arrangement similar to that of FIGS. 7 and 8 in whichactive filter 10′ is located in positive line 14. It is assumed thatmotor arrangement 44 has conveyed to it, via a line 246, signal Us—e.g.a target value for current limitation of motor 12—that is variablebetween 0 and 10 V. Very advantageously, this signal Us can be referreddirectly to negative line 16, which is connected to ground 17. (In FIG.1, Us would be referred to line 14.)

Signal transfer therefore requires no optocouplers or potential-freedifferential amplifiers; this reduces the complexity for such a signaltransfer, e.g. including the transfer of fault signals from motor 12 toa central monitoring system.

FIG. 10 shows a variant 10″ of FIG. 2. It uses an electronic fuse 240configured similarly to fuse 40 of FIG. 2, i.e. if voltage uT at MOSFET24 becomes too high, fuse 240 activates and switches MOSFET 24 off. Incontrast to FIG. 2, however, fuse 240 has an automatic reset function;in other words, in the exemplary embodiment the fuse is automaticallyreset after approx. six seconds. A check is then performed for approx.0.1 seconds as to whether voltage uT is still too high; if so, thesystem again switches off and a new startup attempt is made after aboutsix seconds. If fuse 240 is inadvertently triggered by interference, theresult is to prevent the shutoff from being permanent.

The same reference characters are used for identical or identicallyfunctioning parts in FIG. 10 as in FIG. 2, and those parts are notdescribed again.

Node 114 is connected to the cathode of a Zener diode 250 whose anode isconnected via a resistor 252 to a node 254. The latter is connected tothe cathode of a Zener diode 256 whose anode attaches to negative line16. Node 254 is connected via a resistor 258 to the base of an npntransistor 260 whose emitter is connected to negative line 16 and whosecollector is connected to the base of an npn transistor 262 and, via aresistor 264, to +12 V (Vss).

The collector of transistor 262 is connected to negative input 268 of anoperational amplifier (OA) 266 that is also connected to the regulatedvoltage Vss of e.g. +12 V. Its positive input 270 is connected via aresistor 272 to +12 V and via a resistor 274 to negative line 16. Acapacitor 276 is located between negative input 268 and negative line16. Output 278 of OA 266 is connected via a resistor 280 to positiveinput 270 and via a resistor 282 to negative input 268, and also to theanode of a diode 284 whose cathode is connected via a resistor 286 toinput 268.

Output 278 is connected via a resistor 288 to the base of an npntransistor 290 whose emitter, like the emitter of an npn transistor 292,is connected to negative line 16. The collector of transistor 290 isconnected directly to the base of transistor 292 and, via a resistor294, to +12 V. The collector of transistor 292 is connected to node 32;i.e. when transistor 292 is conductive, node 32 receives a very lowpotential, thus causing current regulator 30 to be blocked.

Manner of Operation of FIG. 10

The reader is referred to the description of FIG. 2 regarding the mannerof operation of current regulator 30, link circuit regulator 34, andovervoltage protector 38.

Fuse 240 with Automatic Reset

If voltage uT rises above a value determined by Zener diodes 250, 256,transistor 260 is switched on, causing transistor 262 to switch off. Thelatter had previously been discharging capacitor 276, and capacitor 276therefore now charges via diode 284 and resistor 286, since the outputof OA 266 is high.

When the voltage at capacitor 276 reaches the threshold voltage atpositive input 270, output 278 switches to low, thereby reducing saidthreshold voltage. Capacitor 276 is now discharged throughhigh-resistance resistor 282 until the voltage at capacitor 276 hasdropped below the (reduced) threshold voltage at positive input 270.

During charging of capacitor 276, the left terminal of resistor 280 isat +12 V; this raises the threshold voltage at positive input 270.

During discharging of capacitor 276, the left input of resistor 280 isat approx. 0 V, so that resistor 280 is connected in parallel withresistor 274 and the threshold voltage at positive input 270consequently decreases. This implements a switching hysteresis.

When output 278 of OA 266 is low, transistor 290 is switched off andtransistor 292 switched on. Because transistor 292 is switched on,target value u32 of current regulator 30 at node 32 goes to zero, andMOSFET 24 is consequently switched off.

This shutoff thus occurs after a short delay due to the charging ofcapacitor 276, e.g. after 100 ms.

After capacitor 276 has discharged through resistor 282, output 278 onceagain becomes high, transistor 290 is conductive, and transistor 292 isblocked, so that current regulator 30 is activated again. If current iis still too high, MOSFET 24 is again switched off after about 100 ms inthe manner already described. If current i is once again normal afterswitching on, current regulator 30 remains switched on, because in thatcase Zener diodes 250, 256 are once again blocked, so that transistor260 is blocked, transistor 262 is conductive, and capacitor 276discharges.

FIG. 11 shows an oscillogram for the case in which, in the context ofFIG. 10, terminals 18 and 20 are short-circuited. MOSFET 24 is brieflyswitched on every six seconds, so that a current i flows in it for 0.1second. Voltage uG at the gate of MOSFET 24 is depicted at the bottom ofFIG. 11. It becomes high only briefly at switch-on if a short circuitstill exists between 18 and 20.

Preferred Values for Components of Electronic Fuse 240

Zener diode 250 BZX284C6V2 Zener diode 252 BZX284C3V9 Resistor 252 33kOhms Resistor 258 1 kOhm Transistors 260, 262, 290, 292 BC846BResistors 264, 274, 288, 294 22 kOhms Resistor 272 330 kOhms Capacitor276 3.3 uF Resistor 286 100 kOhms Diode 284 BAS216 Resistor 282 820kOhms OA 266 LM29020 Resistor 280 43 kOhms

FIG. 12 shows a variant of FIG. 2 or 10. Only the right-hand part ofthese two Figures is therefore depicted.

In FIG. 12, a Zener diode 300 is connected in parallel with MOSFET 24.In such a case a load 302, e.g. a fan, should be connected to terminals18, 20 via a blowout fuse 304. Alternatively, said blowout fuse can bearranged e.g. at a point 306 in supply line 14.

If a DC voltage of 48 V is present between lines 14 and 16, Zener diode300 can be designed, for example, for 28 V, i.e. for approximately halfthe operating voltage.

In terms of defects in MOSFET 24, a distinction must be made between twocases:

a) A short circuit in MOSFET 24. In this case fan 302 continues tofunction but without current regulation.

b) MOSFET 24 is nonconductive. In this case fan 302 would beimmobilized, and the device in question would no longer be cooled.

In this situation, Zener diode 300 becomes conductive and continues tosupply fan 302 with (reduced) power. Assuming a DC voltage of 48 V and aZener diode of 28 V, fan 302 receives a reduced voltage of 20 V, so thatit continues to run but at reduced speed. Zener diode 300 must beselected for the appropriate output, and usually requires a heat sink.

Since electronic fuse 40 or 240 is no longer effective in this case, theadditional blowout fuse 304 is provided in series with fan 302. If theblowout fuse is arranged at point 306, it then provides generalprotection against a short circuit between points 18 and 20.

The arrangement with a Zener diode can, of course, also be used in thecontext of FIG. 7. In this case the Zener diode is arranged betweenpoints 151 and 149. This variant is not explicitly depicted.

Many variants and modifications are of course possible in the context ofthe present invention. Certain additional functions that have beendescribed in connection with the exemplary embodiments could be omittedif applicable, for example the overvoltage protection or electronicfuse, if the customer does not want them. Alternatively, furtheradditional functions are also possible if the customer does want them,e.g. an acoustic or visual alarm in the event of overcurrent or uponactivation of the fuse function.

What is claimed is:
 1. An arrangement for powering a DC motor (12) froma DC power supply, comprising a DC link circuit (14, 22; 16, 141)adapted to be coupled to said DC motor and having a capacitor (21)associated therewith, adapted to temporarily supply energy to said DCmotor; a first regulator (30; 146) for connecting the DC link circuit tothe DC power supply, which feeds a substantially constant current (i)via a transistor (24), serving as a linear adjusting element, to saidcapacitor (21) and to the DC motor; wherein a voltage drop (U_(T))arises at said transistor (24); and further comprising a secondregulator (34; 144) which supplies a target value (U32, U188) to aninput of said first regulator (30; 146), said second regulator having aninput adapted to be supplied with an actual voltage value derived from avoltage (UZK) across said DC motor, whereby said second regulator (34;144) adapts said target value (U32, U188) for said first regulator tovarying loads of the DC motor (12) and thereby minimizes audio-frequencyelectrical fluctuations at supply leads (14, 16) of said motor andminimizes resulting electromagnetic noise.
 2. The arrangement accordingto claim 1, wherein said actual voltage value applied to said input ofsaid second regulator is substantially proportional to the voltage drop(U_(T)) across said transistor (24) serving as said linear adjustingelement.
 3. The arrangement according to claim 2, wherein said voltagedrop (U_(T)) at said transistor (24) corresponds essentially to an ACvoltage component of the voltage at said DC link circuit (10, 22; 16,141).
 4. The arrangement according to claim 1, wherein said target value(U32, U188) for the first regulator (30, 146) is limited to a maximumvalue.
 5. The arrangement according to claim 1, wherein the secondregulator (34, 144) is configured a a proportional regulator with afirst-order timing member.
 6. The arrangement according to claim 5,wherein the second regulator (34, 144) has a larger time constant (T1)than the first regulator (30; 146), causing said second regulator toreact more gradually to change in its input signal than does said firstregulator.
 7. The arrangement according to claim 1, wherein saidtransistor (24) serving as a linear adjusting element is a MOSFETtransistor.
 8. The arrangement according to claim 7, wherein the voltagedrop (U_(T)) at said MOSFET transistor (24; 150) affects, via the secondregulator (34; 144), the target value (U32, U188) applied to said firstregulator.
 9. The arrangement according to claim 7, wherein the voltagedrop (U_(T)) at said MOSFET transistor (24; 150) corresponds essentiallyto an AC voltage component of the voltage (UZK) at the DC link circuit(14, 22; 16, 141).
 10. The arrangement according to claim 1, furthercomprising a circuit (38) which is responsive to a voltage level of saidDC power supply and which, in the event of an overvoltage condition,reduces the current through said first regulator (30, 146).
 11. Thearrangement according to claim 1, further comprising an electronic fuse(40), responsive to a voltage at an adjusting element (24) of the firstregulator (30, 146), and causing a shutoff when said voltage at saidadjusting element exceeds a predetermined value.
 12. The arrangementaccording to claim 11, wherein said electronic fuse (240) has anassociated reset means (260, 262, 276, 282, 284, 286) for reactivatingthe first regulator (30) after lapse of a predetermined time intervalsince shutoff.
 13. The arrangement according to claim 1, furthercomprising a time delay circuit (175) which, for a predetermined periodafter turn-on of the arrangement, deactivates the first regulator (30,146).
 14. The arrangement according to claim 1, further comprising aZener diode (300) connected in parallel to the transistor (24) of thefirst regulator (30, 146), wherein, if a defect causes said transistor(24) to remain non-conductive for more than a predetermined timeinterval, said Zener diode becomes conductive, in order to take over assupplier of current to a DC motor (302) connected to said arrangement.15. The arrangement according to claim 1, wherein said DC motor is anelectronically commutated motor.
 16. The arrangement according to claim1, wherein two conductors (14, 16) connect to said DC power supply, andone of said conductors also serves for signal transmission to or fromsaid connected DC motor (44).
 17. The arrangement according to claim 1,further comprising an additional regulator (52) connected to said DCmotor for controlling an operating value thereof.
 18. An arrangement forpowering a DC motor (12) from a DC power supply, comprising a DC linkcircuit (14, 22; 16, 141) adapted to be coupled to said DC motor andhaving a capacitor (21) associated therewith, adapted to temporarilysupply energy to said DC motor; a first regulator (30; 146) forconnecting the DC link circuit to the DC power supply, which feeds asubstantially constant current (i) via a transistor (24), serving as alinear adjusting element, to said capacitor (21) associated with said DClink circuit and to the DC motor, generating a voltage drop (U_(T)) atsaid transistor (24); and further comprising a second regulator (34;144) which supplies a target value (U32, U188) to an input of said firstregulator (30, 146), said second regulator having a voltage (22),supplied as an actual value to an input of said second regualtor, saidvoltage being substantially proportional to the voltage drop (U_(T)) atsaid transistor (24) serving as said linear adjusting element, thesecond regulator (34; 144) serving to adapt said target value (U32,U188) for said first regulator to varying loads of the DC motor (12) andthereby to minimize audio-frequency electrical fluctuations at supplyleads (14, 16) of said motor and to minimize resulting electromagneticnoise.
 19. The arrangement according to claim 18, wherein said voltagedrop (U_(T)) at said transistor (24) corresponds essentially to an ACvoltage component of the voltage at said DC link circuit (10, 22; 16,141).
 20. The arrangement according to claim 18, wherein said targetvalue (U32, U188) for the first regulator (30, 146) is limited to amaximum value.
 21. The arrangement according to claim 18, wherein thesecond regulator (34, 144) is configured as a proportional regulatorwith a first-order timing member.
 22. The arrangement according to claim21, wherein the second regulator (34, 144) has a larger time constant(T1) than the first regulator (30; 146), causing said second regulatorto react more gradually to change in its input signal than does saidfirst regulator.
 23. The arrangement according to claim 18, wherein saidtransistor (24) serving as a linear adjusting element is a MOSFETtransistor.
 24. The arrangement according to claim 23, wherein thevoltage drop (U_(T)) at said MOSFET transistor (24; 150) affects, viathe second regulator (34; 144), the target value (U32, (U188) applied tosaid first regulator.
 25. The arrangement according to claim 24, whereinthe voltage drop (U_(T)) at said MOSFET transistor (24; 150) correspondsessentially to an AC voltage component of the voltage (UZK) at the DClink circuit (14, 22; 16, 141).
 26. The arrangement according to claim18, further comprising a circuit (38) which is responsive to a voltagelevel of said DC power supply and which, in the event of an overvoltagecondition, reduces the current through said first regulator (30, 146).27. The arrangement according to claim 18, further comprising anelectronic fuse (40), responsive to a voltage at an adjusting element(24) of the first regulator (30, 146), and causing a shutoff when saidvoltage at said adjusting element exceeds a predetermined value.
 28. Thearrangement according to claim 27, wherein said electronic fuse (240)comprises an associated reset means (260, 262, 276, 282, 284, 286) forreactivating the first regulator (30) after lapse of a predeterminedtime interval since shutoff.
 29. The arrangement according to claim 18,further comprising a time delay circuit (175) which, for a predeterminedperiod after turn-on of the arrangement, deactivates the first regulator(30, 146).
 30. The arrangement according to claim 18, further comprisinga Zener diode (300) connected in parallel to the transistor (24) of thefirst regulator (30, 146), wherein, if a defect causes said transistor(24) to remain non-conductive for more than a predetermined timeinterval, said Zener diode becomes conductive, in order to take over assupplier of current to a DC motor (302) connected to said arrangement.31. The arrangement according to claim 18, wherein said DC motor is anelectronically commutated motor.
 32. The arrangement according to claim18, wherein two conductors (14, 16) connect to said DC power supply, andone of said conductors also serves for signal transmission to or fromsaid connected DC motor (44).
 33. The arrangement according to claim 18,further comprising an additional regulator (52) connected to said DCmotor for controlling an operating value thereof.